The disclosure of Japanese Patent Application No. 2001-128363 filed on Apr. 25, 2000, including the specification, drawings and abstract thereof, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a learning control in a hydraulic pressure control apparatus of an automatic transmission and, more particularly, to a learning control that is suitable for use in, for example, a discharge control of the hydraulic pressure that is drained at the time of switching from a running range to neutral (N) in a hydraulic pressure control apparatus of an automatic transmission, in response to an operation of a shift lever or the like.
2. Description of the Related Art
Conventional automatic transmissions (including multi-speed stage automatic transmissions (AT) and continuously variable transmissions (CVT)) have an input clutch hydraulic servo that is supplied with hydraulic pressure (range pressure) from a D-range port of a manual valve. An oil passage connected to the hydraulic servo is provided with a neutral relay valve that is operated by a solenoid valve, and a control valve that is controlled by a linear solenoid valve (see, for example, Japanese Patent Application Laid-Open No. HEI 11-93987).
When the shift lever is moved from the neutral (N) position to the D range position, the line pressure from the D range port of the manual shift valve is supplied to the input clutch hydraulic servo via the control valve and the relay valve. By controlling the control valve via the linear solenoid valve during this operation, the supply of hydraulic pressure is smoothly started, so that shift shock at the time of a N-D shift is prevented.
Conversely, if the shift lever is moved from the D range position to neutral, the relay valve is switched so that the hydraulic pressure of the input clutch hydraulic servo is discharged from the drain port of the manual shift valve via a check valve and an orifice. Due to the amount of flow out of the orifice and the operation of an accumulator, a shock which might otherwise be caused by a rapid torque reduction is prevented.
In the above-described hydraulic pressure control apparatus, the hydraulic pressure on the input clutch is discharged without being controlled at the time of the D-N shift, so that the amount of flow discharged from the input clutch hydraulic servo changes depending on the oil temperature. If the oil temperature is high, a rapid torque reduction may occur causing a shift shock. If the oil temperature is low, the torque on the input clutch is prolonged, to the detriment of shift responsiveness. In that case, it is desirable that the hydraulic pressure of the hydraulic servo be adjusted and controlled. However, pressure adjusting control based on oil temperature or the like varies considerably and thus is insufficiently reliable. In particular, precise control of the discharge from the input clutch hydraulic servo is needed because it muse be performed within the small amount of time before the base pressure of the hydraulic servo is completely discharged from an orifice at the time of a D-N shift.
Accordingly, it is an object of the invention to provide a hydraulic pressure control apparatus of an automatic transmission that solves the aforementioned problems by performing a learning control.
In order to achieve the above objective, the present invention provides an automatic transmission hydraulic pressure control apparatus including valve control means for adjusting and controlling, in accordance with an instruction value, a hydraulic control pressure on a hydraulic servo which, in turn, switches a frictional engagement element between a first state and a second state, e.g., engaged and disengaged, in a shift. The shift may be between different ranges or between different speed stages within the drive range. A detecting means detects the amount of change in rotational speed of a rotating transmission element, which change results from the switch between the first state and the second state. A controller is provided with learning control means for correcting the instruction value for the control valve means based on a comparison between the amount of change in a previous shift and the amount of change resulting from a present switch, e.g., shift. Then, in a next subsequent switch, the instruction value controlling the control valve means is an instruction value as corrected by the learning control means of the controller. The learning control means may also take into account the direction of the immediately previous correction.
In a preferred embodiment, the learning control means includes a plurality of maps for determining a subsequent correction value and a subsequent correcting direction based on the comparison between the previous amount of change and the present amount of change and also based on direction of the immediately previous correction.
The amount of change detected by the detecting means may be a mean value obtained for a plurality of switches or shifts. The learning control operates with a convergence region defined by upper and lower threshold values and where the immediately previous instruction value is outside of the convergence region, that instruction value is corrected to increase the previous amount of change in a direction toward the convergence region. On the other hand, if the immediately previous amount of change, e.g., in the rotational speed of the transmission input shaft, is within the convergence region whereas the present amount of change is outside of the convergence region, the instruction value is corrected by lowering by a predetermined amount.
The amount of change detected by the detecting means may be a change in the rotational speed of the transmission input shaft or, for example, a peak value of rotational acceleration of the input side of the friction engagement element.
Preferably, the controller outputs a predetermined initial value at the time of the switch, e.g., shift, and then outputs a sweep-down at a predetermined sweep angle. That predetermined initial value may be set based on the temperature of oil within the automatic transmission.
In the preferred embodiment, the value control means includes a first control valve disposed between the hydraulic servo and a running range port of the manual shift valve and a second control valve that controls the first control valve by adjusting a control pressure to the first control valve, which control pressure is based on the instruction value from the controller. The first and second control valves may be disposed in an oil passage in parallel with another oil passage providing a direct fluid connection between the hydraulic servo and the running range port and having therein an orifice and a check valve.